x265: enable multibitdepth on aarch64-linux

[JamieMagee]

The multibitdepthSupport parameter currently excludes aarch64-linux:

multibitdepthSupport ? (
  stdenv.hostPlatform.is64bit && !(stdenv.hostPlatform.isAarch64 && stdenv.hostPlatform.isLinux)
),

This exclusion was added with the original multibitdepth support in #92052 (2020), back when x265 3.x didn't have 10-bit or 12-bit aarch64 assembly primitives. The PFX macro would expand to symbols like x265_12bit_pixel_satd_4x4_neon that didn't exist, causing link failures (see #154347 for details).

x265 has had working aarch64 HBD support since 4.0 (release notes).

Without multibitdepth, the only supported pixel format on aarch64 is yuv420p (8-bit). Any 10-bit input, which is common from modern cameras, causes ffmpeg's libx265 encoder to fail with:

[libx265] Invalid video pixel format: -1

I hit this running Home Assistant's stream component on a Raspberry Pi 5. Camera streams using HEVC would crash in PyAV's avcodec_open2(libx265) call.

This PR removes the aarch64-linux exclusion so multibitdepthSupport is just stdenv.hostPlatform.is64bit.

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

[github-actions]

The PR's base branch is set to master, but this PR causes 13832 rebuilds.
It is therefore considered a mass rebuild.
Please change the base branch to the right base branch for your changes (probably staging).

[github-actions]

The PR's base branch is set to staging, but 8 commits from the master branch are included. Make sure you know the right base branch for your changes, then:

• If the changes should go to the master branch, change the base branch.
• If the changes should go to the staging branch, rebase your PR onto the correct merge-base:

  # git rebase --onto $(git merge-base upstream/staging HEAD) $(git merge-base upstream/master HEAD)
  git rebase --onto 46ca68c26436e0678e396ce7acd756d482401942 22874fc8a1c78712f082120ae9555eb57cd57dd1
  git push --force-with-lease